To that end, I'll be calculating each show's relative ratings Renew / Cancel Index as follows:

Instead of the numerator of the Index being a show’s overall 18-49 average, it will just be its new episode 18-49 average. That eliminates the problem comparing shows with very different numbers of repeat episodes.

Instead of the denominator of the Index being a network’s overall 18-49 average, it will just be the scripted show new episode adults 18-49 average. That eliminates the problems associated with averages being influenced by sports, reality and news programming.

I can begin the calculations as soon as new shows start airing in September (which for the CW has been several weeks prior to the start of the official "season").

I will start a "Spring Only" relative average for each show beginning after the week that includes New Year's Day 2011. That produced somewhat better predictive capabilities than keeping a single year long relative calculation.

How would that method have done in the 2009-10 season?

At least as well (perhaps a bit better than) the earlier method in prediction, while meeting all my other objectives above.

A Renew / Cancel line somewhere between 0.80-0.86 with the new calculation method would have predicted every show except:

Friday Night Lights - no less predictive than before, not sure how other than exception noting a subsidized show can be worked into the calculations

Medium - would not have done any better a job predicting the different fates for Medium and Ghost Whisperer. Exception noting advantage for network produced shows likely the only answer here too.

90210 - would have been better predicted had I used adults 18-34 or women 18-34 ratings for the CW shows only, which I likely will.

Romantically Challenged - no better or worse than predicting using the old method. A retentionistas revenge show, canceled with ratings above what would be OK except in its advantaged timeslot.

Accidentally on Purpose, Heroes (perhaps Human Target, V) - shows close to the Renew / Cancel "line" will always be tricky, the "line" is, as in the past, more of a "zone".

24 - old, expensive shows with better than average ratings are no better predicted than before.

Here's how the new "post New Year's relative Index" would have worked out through early May this season, when the networks were about to make their final decisions, with renewed shows in bold.